1.全屏显示

var dem = document.documentElement;
//W3C  
if (docElm.requestFullscreen) {  
     docElm.requestFullscreen();  
}
//FireFox  
else if (docElm.mozRequestFullScreen) {  
     docElm.mozRequestFullScreen();  
}
//Chrome  
else if (docElm.webkitRequestFullScreen) {  
     docElm.webkitRequestFullScreen();  
}
//IE 11
else if (elem.msRequestFullscreen) {
   elem.msRequestFullscreen();
}

2、退出全屏

if (document.exitFullscreen) {  
     document.exitFullscreen();  
}  
else if (document.mozCancelFullScreen) {  
     document.mozCancelFullScreen();  
}  
else if (document.webkitCancelFullScreen) {  
     document.webkitCancelFullScreen();  
}
else if (document.msExitFullscreen) {
       document.msExitFullscreen();
}